140 powermax lockout

Hi Mike,  my name is John I'm a heating engineer I have a boiler in an apartment at the Borough High street London. The boiler operates in heating and hot water mode but then goes to lock-out. I can isolate the electrics, restart and then it fires up. Sometimes it will take 2-3 times to fire -up and on doing so I can hear a poping noise when trying to fire. The gas pressure and working pressure is fine. Sometimes it can work for days without going off. I got a feeling it could be the gas valve or it could be the elecrode on the burner but I'm not sure, having never worked on these boilers before.

Could you give me a quote to service the boiler and replace any parts you may think it needs.

I wait you reply

John